This invention relates in general to fluid control valves. In particular, this invention relates to an improved two-stage fluid control valve that includes a first stage mechanical valve and a second stage microvalve, such as for use in a system that requires a positive shut-off function.
MEMS (Micro Electro Mechanical Systems) are a class of systems that are physically small, having features with sizes in the micrometer range, i.e., about 10 μm or smaller. These systems have both electrical and mechanical components. The term “micromachining” is commonly understood to mean the production of three-dimensional structures and moving parts of MEMS devices. MEMS originally used modified integrated circuit (computer chip) fabrication techniques (such as chemical etching) and materials (such as silicon semiconductor material) to micromachine these very small mechanical devices. Today, there are many more micromachining techniques and materials available. The term “micromachined device” as used in this application means a device having some features with sizes of about 10 μm or smaller, and thus by definition is at least partially formed by micromachining. More particularly, the term “microvalve” as used in this application means a valve having features with sizes of about 10 μm or smaller, and thus by definition is at least partially formed by micromachining. The term “microvalve device” as used in this application means a micromachined device that includes a microvalve, and that may include other components. It should be noted that if components other than a microvalve are included in the microvalve device, these other components may be micromachined components or standard sized (larger) components. Similarly, a micromachined device may include both micromachined components and standard sized (larger) components.
Various microvalve devices have been proposed for controlling fluid flow within a fluid circuit. A typical microvalve device includes a displaceable member or valve component movably supported by a body for movement between a closed position and a fully open position. When placed in the closed position, the valve component substantially blocks or closes a first fluid port that is otherwise in fluid communication with a second fluid port, thereby preventing fluid from flowing between the fluid ports. When the valve component moves from the closed position to the fully open position, fluid is increasingly allowed to flow between the fluid ports.
U.S. Pat. Nos. 6,523,560; 6,540,203; and 6,845,962, the disclosures of which are incorporated herein by reference, describe microvalves made of multiple layers of material. The multiple layers are micromachined and bonded together to form a microvalve body and the various microvalve components contained therein, including an intermediate mechanical layer containing the movable parts of the microvalve. The movable parts are formed by removing material from the intermediate mechanical layer (by known micromachined device fabrication techniques, such as, but not limited to, deep reactive ion etching) to create a movable valve element that remains attached to the rest of the part by a spring-like member. Typically, the material is removed by creating a pattern of slots through the material to achieve the desired shape. The movable valve element will then be able to move in one or more directions an amount roughly equal to the slot width.
U.S. Pat. No. 7,156,365, the disclosure of which is also incorporated herein by reference, describes a method of controlling the actuator of a microvalve. In the disclosed method, a controller supplies an initial voltage to the actuator which is effective to actuate the microvalve. Then, the controller provides a pulsed voltage to the actuator which is effective to continue the actuation of the microvalve.
Conventional gas ranges and gas ovens use fluid control valves to control the flow of natural gas or propane to one or more burners on a stovetop and in an oven, respectively. These conventional gas ranges and ovens require precise flame or temperature control and a positive shut-off function in the flow control valve to prevent an unwanted and potentially hazardous flow of natural gas or propane when the gas range or oven burners are in an off position. Additionally, the process of controlling the flow of gas in silicon fabrication, such as in the fabrication of silicon wafers for MEMS microvalves, microchips, and the like, also requires a positive shut-off function to prevent defects in the fabrication process.
Conventional MEMS microvalves are known to provide very accurate fluid flow control, but typically experience a small amount of fluid leakage during normal operation, and are therefore unsuitable as a stand-alone flow control valve for use in a gas range application.
It would therefore be desirable to provide a two-stage fluid control valve having a second stage microvalve combined with a first stage mechanical valve that has an improved positive shut-off function.